RU2575947C2 - Simulation of interaction between frac job fractures in system of complex fractures - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: claimed process comprises the accessing of data on the well location, construction of geological medium mechanical model and patterning of frac job fractures growth in the system of fractures in time. Said patterning comprises propagation of said fractures from the drill hole and in the underground seam fractures for formation of the system of frac job fractures. Parameters of the latter are defined after propagation. Transfer parameters are defined for proppant to be forced through the system of said frac job fractures. Sizes of the latter are defined proceeding from their parameters and mechanical model of geological medium. Besides, claimed process comprises the shadowing of strain relative to frac job fractures for determination of relative influence of strains between the fractures and reiteration of patterning proceeding from the defined interrelation of fractures. Also, this process can include the determination of the intersection pattern.

EFFECT: higher efficiency of simulation.

17 cl, 32 dwg, 4 tbl

Description

In general, the present disclosure relates to methods and systems for performing work at a well location. More specifically, this disclosure relates to methods and systems for performing hydraulic fracturing, such as examining underground formations and characterizing hydraulic fracturing systems in an underground formation.

To facilitate hydrocarbon production from oil and gas wells, hydraulic fracturing of underground formations surrounding such wells can be performed. Hydraulic fracturing can be used to create cracks in subterranean formations to allow the movement of oil or gas to the well. The formation is fractured by introducing a specially designed fluid (referred to in this application as “hydraulic fracturing fluid” or “hydraulic fracturing suspension”) at high pressure and at high flow rates into the reservoir through one or more boreholes. Hydraulic fractures can propagate from a borehole hundreds of feet in two different directions in accordance with natural stresses in the formation. Under certain conditions, they can form a system of complex cracks. Complex fracture systems may include artificially generated hydraulic fractures and natural fractures that may or may not intersect along multiple azimuths, in numerous planes and directions, and in numerous areas.

Modern methods and systems for monitoring hydraulic fractures can map the places where cracks occur and the propagation of cracks. In some methods and systems of microseismic monitoring, the positions of seismic events can be processed by converting the arrival times of seismic waves and polarization information into three-dimensional space using simulated travel times and / or ray paths. These methods and systems can be used to predict the development of hydraulic fractures over time.

Patterns of hydraulic fractures created by impacting the formation to form cracks can be complex and can constitute a system of cracks displayed by the distribution of related microseismic events. To represent the hydraulic fractures created, models of complex hydraulic fracture systems have been developed. Examples of models of cracks are presented in US patents No. 6101447, 7363162, 7788074 and in applications No. 2008/0133186, 2010/0138196 and 2010/0250215 for US patents.

SUMMARY OF THE INVENTION

At least one aspect of the present disclosure relates to methods for performing a fracturing operation at a well location. The location of the well is in the subterranean formation, thereby having a borehole and a system of fractures. The crack system has natural cracks. The location of the well can be excited by injecting the injected fluid with the proppant into the fracture system. The method includes obtaining data on the location of the well containing parameters of natural fractures, and obtaining a mechanical model of the geological environment for the subterranean formation, and forming a picture of the growth of hydraulic fractures for the fracture system over time. The formation includes the propagation of hydraulic fractures from the borehole and into the fracture system of the subterranean formation to form a system of hydraulic fractures, including natural and hydraulic fractures, determination of the parameters of hydraulic fractures after propagation, determination of transfer parameters for the proppant passing through hydraulic fracture system, and determining the size of hydraulic fractures based on certain parameters ditch cracks, certain transfer parameters and a mechanical model of the geological environment. In addition, the method includes performing voltage shading relative to hydraulic fractures to determine the mutual influence of stresses between hydraulic fractures and repeating the formation based on a certain mutual influence of stresses.

If hydraulic fractures occur with a natural fracture, the method may also include determining the nature of the intersection between hydraulic fractures and the encountered crack based on a certain mutual influence of the cracks, and repetition may include repeating the formation based on a certain mutual influence of stresses and the nature of the intersection. In addition, the method may include stimulating the location of the well by injecting the injected fluid with the proppant into the fracture system.

In addition, the method may include, if the fracture of the hydraulic formation meets a natural fracture, determining the nature of the intersection with the encountered natural fracture, and in the method the repetition comprises repeating the formation based on a certain mutual influence of stresses and the nature of the intersection. The pattern of crack growth may or may not change due to the nature of the intersection. The hydraulic fracture pressure of the hydraulic fracture system can be greater than the stress acting on the encountered crack, and the pattern of crack growth can propagate along the encountered crack. The pattern of crack growth can continue to propagate along the crack encountered until it reaches the end of the natural crack. The pattern of crack growth can change direction at the end of a natural crack and the pattern of crack growth can continue in a direction perpendicular to the minimum stress at the end of a natural crack. The pattern of crack growth can propagate perpendicular to the local principal stress in accordance with the shading of the stress.

Shading stresses may include performing displacement fractures for each of the hydraulic fractures. Shading stresses may include performing shading stresses around multiple boreholes at the location of the wells and repeating the formation using shading stresses performed on numerous boreholes. Voltage shadowing may include performing voltage shadowing at numerous excitation steps in a borehole.

In addition, the method may include validating the pattern of crack growth. Validation may include comparing the crack growth pattern with at least one simulation from simulations of the crack system.

Propagation may include the propagation of hydraulic fractures throughout the fracture growth pattern based on the parameters of natural fractures and the minimum stress and maximum stress acting on the subterranean formation. Determining the size of the cracks may include one of the evaluation of seismic measurements, tracking the movement of ants, acoustic measurements, geological measurements, and combinations thereof. Data on the location of the well may include at least one of geological, petrophysical, geomechanical data, logging data, well completion, historical data, and combinations thereof. The parameters of natural fractures can be formed by one of the observation of downhole logging images, estimating the size of the fractures based on downhole measurements, obtaining microseismic images and combinations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of a system and method for characterizing downhole stresses will be described with reference to the accompanying drawings. For the designation of similar features and components throughout the drawings, the same reference numbers are used. In the drawings:

FIG. 1.1 is a schematic illustration of a hydraulic fracturing site showing a fracturing operation;

FIG. 1.2 is a schematic illustration of a hydraulic fracturing site showing microseismic events;

FIG. 2 is a schematic view of a two-dimensional crack;

FIG. 3.1 is a schematic illustration of the effect of a voltage shadow;

FIG. 3.2 is a schematic illustration of the discontinuities Ds and Dn;

FIG. 4 is a schematic view of two parallel rectilinear cracks for comparing the two-dimensional method of discontinuous displacements and three-dimensional fast Lagrange analysis of continuous media;

FIG. 5.1-5.3 are graphs illustrating stresses at various places for extended cracks obtained by the two-dimensional method of discontinuous displacements and three-dimensional fast Lagrange analysis of continuous media;

FIG. 6.1, 6.2 are graphs showing the development paths of two initially parallel cracks in an isotropic and anisotropic stress field, respectively;

FIG. 7.1, 7.2 are graphs showing the development paths of two initially spaced cracks in an isotropic and anisotropic stress field, respectively;

FIG. 8 is a schematic view of transverse parallel fractures along a horizontal well;

FIG. 9 is a graph showing the length of five parallel cracks;

FIG. 10 is a schematic view of parallel cracks from FIG. 9 showing the geometry and width of the cracks in accordance with an unconventional model of cracks;

FIG. 11.1, 11.2 are schematic diagrams showing the geometry of cracks for the case of high pressure drop across the perforations and the case of large spacing of cracks, respectively;

FIG. 12 is a graph showing the mapping of microseismic events;

FIG. 13.1-13.4 are schematic diagrams illustrating a simulated crack system in comparison with microseismic measurements in steps 1-4, respectively;

FIG. 14.1-14.4 are schematic diagrams showing a system of distributed cracks at various stages;

FIG. 15 is a flowchart showing a method of performing a fracturing operation; and

FIG. 16.1-16.4 are schematic illustrations showing the growth of cracks around a borehole during a hydraulic fracturing operation.

DETAILED DESCRIPTION OF THE INVENTION

The description that follows includes examples of devices, methods, techniques and sequences of instructions that implement the methods according to the subject invention. However, it is understood that the described embodiments may be practiced without these specific details.

To get an idea of the systems of underground cracks, models are developed. Various factors and / or data may be taken into account in the models so that the models cannot be constrained by taking into account the amount of injected fluid or the mechanical interactions between the cracks and the injected fluid, as well as between the cracks. Constrained models can be created to provide a general idea of the mechanisms involved, but the mathematical description may be complex and / or computer processing resources and time may be required to perform accurate simulations of the development of hydraulic fractures. A constrained model can be configured to perform simulations taking into account factors such as the interaction between cracks over time and in accordance with specified conditions.

An unconventional model of fractures (NMT) (or a complex model) can be used to simulate the development of a system of complex fractures in a formation with existing natural fractures. Numerous branches of cracks can develop along the way and with crossing / crossing each other. Each open crack can cause additional stresses in the surrounding rock and adjacent cracks, and this can be called the effect of "shadow stress". The stress shadow can cause crack parameters to be limited (for example, width), which can lead, for example, to a greater likelihood of proppant loss. In addition, the trajectory of the development of cracks can change under the shadow of stress and can affect the patterns of the crack system. The stress shadow can influence the modeling of crack interaction in a complex model of cracks.

A method for calculating the stress shadow in a system of complex hydraulic fractures is proposed. The method can be performed on the basis of an improved two-dimensional method of discontinuous displacements (DLS) with correction for the influence of the final crack height or three-dimensional method of discontinuous displacements (TMPC). The stress field calculated by the two-dimensional method of discontinuous displacements can be compared with the results of three-dimensional numerical simulation (three-dimensional method of discontinuous displacements or three-dimensional method of fast Lagrange analysis of continuous media) to determine the approximation for the three-dimensional problem of cracks. This calculation of the stress shadow can be included in an unconventional model of cracks. The results for simple cases of two cracks show that cracks can be attracted or repelled from each other depending, for example, on their initial relative positions, and these results can be compared with an independent two-dimensional model of non-planar hydraulic fractures.

Additional examples of the development of planar and complex cracks from clusters of perforations are presented, showing that the interaction of cracks can affect the size of cracks and the pattern of development. In a formation with a small stress anisotropy, the interaction of cracks can lead to a significant difference in the cracks, since they can tend to repel each other. However, even when the stress anisotropy is large and the rotation of the crack due to the interaction of the cracks is limited, stress shadowing can have a strong effect on the crack width, and this can affect the distribution of injection rates into numerous perforation clusters and therefore the general geometry of the crack system and proppant placement.

In FIG. 1.1 and 1.2 show the development of cracks around the well location 100. At the location of the well, there is a borehole 104 extending from the wellhead 108 at the surface and below through the subterranean formation 102. A fracture system 106 extends around the borehole 104. A pump system 129 is located near the wellhead 108 to allow fluid to flow through the tubing string 142 .

The pump system 12 9 is shown controlled by a field operator 127, recording production and operational field data and / or performing work in accordance with the established pumping schedule. Pumping system 129 pumps fluid from a surface into borehole 104 during a hydraulic fracturing operation.

The pump system 129 may include a water source, such as a plurality of water tanks 131, from which water is supplied to the gel hydration unit 133. In a gel hydration unit 133, water from tanks 131 is combined with a gelling agent to form a gel. The gel is then fed into a mixer 135, in which it is mixed with proppant from proppant transport means 137 to form a hydraulic fracturing fluid. A gelling agent can be used to increase the viscosity of the fracturing fluid and so that the proppant can be suspended in the fracturing fluid. In addition, it can act as a friction reducing agent, allowing for higher injection rates with less friction pressure loss.

Next, the hydraulic fracturing fluid is pumped out from the mixer 135 into the tanker 120 for processing, equipped with plunger pumps, shown by solid lines 143. In each tanker 120 for processing, the hydraulic fracturing fluid is received at low pressure, and is discharged, which is shown by dotted lines 141, from it into a common manifold 139 (sometimes called a "rocket supercharger on a trailer" or "rocket supercharger") under high pressure. Further, the “rocket supercharger” 139 sends, as shown by solid line 115, hydraulic fracturing fluid from tankers 120 for processing to borehole 104. One or more processing tankers 120 can be used to supply hydraulic fracturing fluid at a given speed.

Each processing tanker 120 can typically operate at any speed, for example, with a corresponding maximum operating capacity. When operating tankers 120 for processing with a working capacity, one can be allowed to fail and the remaining ones to work at a higher speed to compensate for the absence of a failed pump. Computerized control system 149 can be used to control the entire pumping system 129 during a fracturing operation.

Various fluids, such as conventional reservoir fluids along with proppants, can be used to create cracks. Other fluids, such as viscous gels, a water-based reagent (which may have a friction reducer (polymer) and water), can also be used for hydraulic fracturing in shale gas wells. Such a water-based reagent can be in liquid form (for example, with almost the same viscosity as water) and can be used to create more complex cracks, such as the numerous microseismic cracks detected during monitoring.

As also shown in FIG. 1.1 and 1.2, the fracture system includes fractures located at various locations around the borehole 104. The various fractures may be natural fractures 144 that were present prior to the injection of fluids, or fractures 146 that formed in the formation 102 during injection. In FIG. 1.2 shows a system 106 of cracks, determined by microseismic events 14 8 collected using conventional means.

Multi-stage modeling may be the norm when developing unconventional reservoirs. However, an obstacle to optimizing openings in clay reservoir strata may be the absence of hydraulic fracture models that can adequately simulate the development of complex fractures, often observed in these strata. A model of a complex fracture system (or an unconventional fracture model) was developed (see, for example, Weng X., Kresse O., Wu R. and Gu H., "Modeling of hydraulic fracture propagation in a naturally fractured formation", Paper SPE 140253 , presented at the SPE Hydraulic Fracturing Conference and Exhibition, Woodlands, Texas, USA, January 24-26 (2011) (hereinafter "Weng 2011"); Kresse O., Cohen S., Weng Χ., Wu R. and Gu H., 2011 (hereinafter "Kresse 2011"), "Numerical modeling of hydraulic fracturing in naturally fractured formations", 45th Rock Mechanics / Geomechanics Symposium, San Francisco, CA, June 26-29, full contents of the sources are included in this application) .

Existing models can be used to simulate the development of cracks, deformation of the rock and the flow of fluid into the system of complex cracks created during processing. In addition, the model can be used to solve the fully connected problem of fluid flowing into a system of cracks and elastic deformation of cracks, for which one can have the same assumptions and governing equations as in the usual pseudo-three-dimensional model of cracks. Transfer equations can be solved for each component of injected fluids and proppants.

Using conventional planar crack models, various aspects of a crack system can be modeled. The proposed unconventional model of cracks also includes the ability to simulate the interaction of hydraulic fractures with existing natural fractures, that is, it can be determined that a hydraulic fracture develops unhindered or is retained by a natural fracture when they intersect, and subsequently develops along a natural fracture. The branching of a hydraulic fracture at the intersection with a natural fracture may give rise to the development of a complex fracture system.

The intersection model can be extended based on the Renshaw and Polland criterion for intersection of the interface (see, for example, Renshaw CE. And Polland DD, 1995, "An experimentally verified criterion for propagation across unbounded frictional interfaces in brittle, linear elastic materials", Int. J . Rock Mech. Min. Sci. And Geomech. Abstr., 32: 237-249 (1995), the full content of the source is included in this application) so that it can be applied to any intersection angle and improved (see, for example, Gu H . and Weng X., "Criterion for fractures crossing frictional interfaces at non-orthogonal angles", 44th US Rock symposium, Salt Lake City, Utah, June 27-30, 2010 (hereinafter Gu and Weng 2010), full contents source included in this application by reference), and confirmed by experimental data (see, for example, Gu H., Weng X., Lund J., Mack M., Ganguly U. and Suarez-Rivera R., 2011, "Hydraulic fracture crossing natural fracture at non-orthogonal angles, A criterion, its validation and applications ", Paper SPE 139984, presented at the SPE Hydraulic Fracturing Conference and Exhibition, Woodlands, Texas, January 24-26 (2011) (hereinafter" Gu et al. 2011 "), the full content of the source is incorporated into this application by reference), and included in the unconventional model of cracks.

To properly simulate the development of multiple or complex cracks in the model of cracks, the interaction between adjacent branches of hydraulic fractures, often called the stress shadow effect, can be taken into account. When a single planar hydraulic fracture opens at a finite net fluid pressure, a stress field that is proportional to the net pressure can be applied to the surrounding rock.

For the limited case of a vertical crack of infinite length and constant finite height, one can obtain an analytical expression for the stress field caused by an open crack. See, for example, Warpinski N.F. and Teufel L.W., "Influence of geologic discontinuous on hydraulic fracture propagation", JPT, Feb., 209-220 (1987) (hereinafter Warpinski and Teufel) and Warpinski N.R. and Branagan P.T., "Altered-stress fracturing", SPE JPT, September, 1989, 990-997 (1989), the full contents of the sources are incorporated into this application by reference). The net pressure (or more precisely, the pressure at which the crack opens) can cause compressive stress in the direction perpendicular to the crack, in addition to the minimum local stress, which can be equal to the net pressure on the surface of the crack, but quickly decreases with distance from the crack.

At a distance in excess of one crack height, the induced stress can be just a small part of the net pressure. Therefore, the term “stress shadow” can be used to describe this increase in stress in the region surrounding the crack. If the second hydraulic fracture is created parallel to the existing open crack and if it falls into the shadow of the stress (i.e., the distance to the existing crack is less than the height of the crack), then the second crack will actually perceive a closing stress exceeding the initial local stress. As a consequence, a higher pressure may be required to develop the crack and / or the crack may have a smaller width than the width of the corresponding single crack.

One application of stress shadow analysis may include calculating and optimizing distances between multiple fractures that are simultaneously developing from a horizontal borehole. In clay formations with very low permeability, cracks can be located close to each other for efficient drainage of the reservoir. However, the effect of the stress shadow can inhibit the development of a crack in the immediate vicinity of other cracks (see, for example, Fisher M.K., Heinze JR, Harris CD., Davidson Β.M., Wright C.A. and Dunn K.P. , "Optimizing horizontal completion technique in the Barnett shale using microseismic fracture mapping", SPE 90051, presented at the SPE Annual Technical Conference and Exhibition, Houston, 26-29 September 2004, the full contents of the source are incorporated into this application by reference).

Studies on the mutual influence of parallel cracks have been performed previously (see, for example, Warpinski and Teufel; Britt LK and Smith M.V., "Horizontal well completion, stimulation, optimization and risk mitigation", Paper SPE 125526, presented at the 2009 SPE Eastern Regional Meeting, Charleston, September 23-25, 2009; Cheng Y, 2009, "Boundary element analysis of the stress distribution around multiple fractures: Implications for the spacing of perforation clusters of hydraulically fractured horizontal wells", Paper SPE 125769, presented at the 2009 SPE Eastern Regional Meeting, Charleston, September 23-25, 2009; Meyer BR and Bazan LW, "A discrete fracture network model for hydraulically induced fractures: Theory, parametric and case studies, Paper SPE 140514, presented at the SPE Hydraulic Fracturing Conference and Exhibition, Woodlands, Texas, USA, January 24-26, 2011; Roussel NP and Sharma MM, "Optimizing frac ture spacing and sequencing in horizontal-well fracturing ", SPEPE, May, 2011, pp. 173-184, the full contents of the sources are incorporated into this application by reference). Studies cover parallel cracks in static conditions.

The result of the stress shadow can be a smaller crack width in the middle region of numerous parallel cracks due to increased compressive stresses from neighboring cracks (see, for example, Germanovich LN and Astakhov D., "Fracture closure in extension and mechanical interaction of parallel joints", J. Geophys. Res., 109, B02208, doi: 10.1029 / 2002, JB002131 (2004); Olson JE, "Multi-fracture propagation modeling: Applications to hydraulic fracturing in shales and tight sands", 42nd US Rock Mechanics Symposium and 2nd US- Canada Rock Mechanics Symposium, San Francisco, CA, June 29 - July 2, 2008, full contents of the sources are incorporated into this application by reference). When multiple cracks develop simultaneously, the distribution of the rates of flow into the cracks can be a dynamic process and can be influenced by the net pressure of the cracks. The net pressure can strongly depend on the width of the crack and, therefore, the influence of the pressure shadow on the distribution of the inflow velocities and the size of the cracks needs further investigation.

In addition, the dynamics of simultaneously developing multiple cracks may depend on the relative positions of the initial cracks. If the cracks are parallel, for example in the case of multiple cracks that are orthogonal to the horizontal borehole, the cracks can repel from each other, resulting in a curvature of the cracks to the outside. However, if multiple cracks are spaced, for example, cracks starting from a horizontal borehole that are not perpendicular to the fracture plane, the interaction between adjacent cracks can be such that their ends are attracted to each other and even join (see, for example, Olson J .Ε., "Fracture mechanics analysis of joints and veins", PhD dissertation, Stanford University, San Francisco, California (1990); Yew CH., Mear Μ. Ε., Chang C.C. and Zhang X.C., On perforation and fracturing of deviated cased wellbores ", Paper SPE 26514, presented at SPE 68th Annual Technical Conference and Exhibition, Houston, TX, Oct. 3-6 (1993); Weng X.," Fracture initiation and propagation from deviated wellbores " , Pa per SPE 26597, presented at SPE 68th Annual Technical Conference and Exhibition, Houston, TX, Oct. 3-6 (1993), full contents of the sources are incorporated into this application by reference).

When a hydraulic fracture crosses a secondary crack oriented in the other direction, it can cause an additional closing stress of the secondary crack, which is proportional to the net pressure. This stress can be determined and taken into account when calculating the crack opening pressure when analyzing a pressure-dependent leak in a fractured formation (see, for example, Nolte K., "Fracturing pressure analysis for nonideal behavior", JPT, Feb. 1991, 210-218 (SPE 20704) (1991) (hereinafter "Nolte 1991"), the full contents of the source are incorporated into this application by reference).

For more complex cracks, a combination of the interactions of the various cracks discussed above can be proposed. To properly account for these interactions and maintain computational efficiency so that they can be included in the model of a complex crack system, an appropriate modeling framework can be created. The method, based on the advanced two-dimensional method of discontinuous displacements (DLS), can be used to calculate stresses induced on a given crack and rock from the rest of the complex crack system (see, for example, Olson J.Ε., "Predicting Fracture Swarms - The Influence of Sub critical Crack Growth and the Crack-Tip Process Zone on Joints Spacing in Rock. In The Initiation, Propagation and Arrest of Joints and Other Fractured, ed. JW Cosgrove and T. Engelder, Geological Soc. Special Publications, London, 231, 71-78 (2004) (hereinafter "Olson 2004"), the full content of the source is incorporated into this application by reference). In addition, the crack rotation can be modeled on the basis of and the changing direction of local stress in front of the end of the developing crack.The results of modeling from an unconventional model of cracks, which include modeling of interaction, are presented.

Description of the unconventional model of cracks

To simulate the development of a system of complex cracks, which consists of many intersecting cracks, one can use equations that determine the fundamental physical properties of the crack formation process. The main constitutive equations may include, for example, equations determining the flow of fluid into a system of cracks, equations determining the deformation of cracks, and a criterion for the development / interaction of cracks.

For the continuity equation, it is assumed that the fluid flow passes through a system of cracks while maintaining mass in accordance with:

- средняя ширина или раскрыв в поперечном сечении трещины на месте s=s(x,y), H_f1 - высота жидкости в трещине и q_L - объемная скорость утечки через стенку трещины гидравлического разрыва в матрицу на единицу высоты (скорость, с которой разрывающая жидкость просачивается в окружающую проницаемую среду), которая представлена в модели утечки Картера. Концы трещин распространяются как резкий фронт, а длина трещины гидравлического разрыва в любой данный момент t времени определяется как l(t).where q is the local flow velocity inside the hydraulic fracture along the length, $$\overline{w}$$

is the average width or opening in the cross section of the crack in place s = s (x, y), H _f1 is the height of the fluid in the crack, and q _L is the volumetric leakage rate through the hydraulic fracture wall into the matrix per unit height (the speed at which the fracturing fluid seeps into the surrounding permeable medium), which is presented in the Carter leakage model. The ends of the cracks propagate as a sharp front, and the length of the hydraulic fracture at any given time t is defined as l (t).

The properties of the working fluid can be determined by an exponent n ′ (an indicator of fluid motion) and an indicator K ′ consistency. The fluid flow through the proppant pack may be laminar, turbulent, or Darcy flow, and may accordingly be described by various laws. For the general case of a one-dimensional laminar flow in any given crack branch, one can use the Poiseuille law (see, for example, Nolte, 1991):

Where

In this case, w (z) represents the crack width as a function of depth at the current position s, α is the coefficient, n is an exponent (fluid consistency index), ϕ is the shape function, and dz is the integration increment in the formula along the crack height.

The width of the crack can be related to the fluid pressure through the equation of elasticity. The elastic properties of the rock (which for the most part can be considered homogeneous, isotropic, linear elastic material) can be determined through Young's modulus E and Poisson's ratio v. In the case of a vertical crack in a layered medium with an alternating minimum horizontal stress σ _h (x, y, z) and fluid pressure p, the profile (w) of the width can be determined from the analytical solution in the form:

where w is the crack width at a point with spatial coordinates x, y, z (coordinates of the center of the element of the crack); p (x, y) is the fluid pressure, H is the height of the crack element and z is the vertical coordinate along the crack element at the point (x, y).

Since the height of the cracks can vary, a calculation of the height increment described, for example, in Kresse 2011 can also be included in the system of governing equations.

In addition to the equations presented above, the global condition of volume balance can be satisfied:

where g _L is the fluid leakage rate, Q (t) is the time-dependent injection rate, H (s, t) is the crack height at the point s (x, y) of space and at time t, ds is the length increment when integrated over crack length, dh ₁ is the increment of the leakage height, H _L is the leakage height and s ₀ is the jet loss coefficient. Equation (5) establishes that the total volume of fluid injected during time t is equal to the volume of fluid in the system of cracks and the volume flowing out of the cracks at time t. In this case, L (t) represents the total length of the developed hydraulic fractures at time t and S ₀ is the jet loss coefficient. For boundary conditions, it may be required that the flow rate, net pressure, and crack width be zero at the ends of all cracks.

The system of equations 1-5 together with the initial and boundary conditions can be used to represent the system of governing equations. The combination of these equations and the discretization of the system of cracks into small elements can lead to a nonlinear system of equations taking into account the fluid pressure p in each element, which simplifies at f (p) = 0, which can be solved using the damped Newton-Raphson method.

The interaction of cracks can be taken into account when modeling the development of hydraulic fractures in reservoirs with natural fractures. It includes, for example, the interaction between hydraulic fractures and natural fractures, as well as the interaction between hydraulic fractures. For the interaction between hydraulic fractures and natural fractures in an unconventional model of fractures, a semi-analytical intersection criterion can be implemented using, for example, the approach described in Gu and Weng 2010 and in Gu et al. 2011.

Stress shadow modeling

In the case of parallel cracks, the stress shadow can be represented as a superposition of stresses from neighboring cracks. In FIG. 2 schematically shows a two-dimensional crack 200 in a coordinate system having an x axis and an y axis. Different points along the two-dimensional crack, such as the first end at h / 2, the second end at -h / 2 and the midpoint, are connected by lines to the observation point (x, y). Lines L, L ₁ , L ₂ extend at angles θ, θ ₁ , θ ₂ from points along a two-dimensional crack to the observation point.

The stress field around a two-dimensional crack with an internal pressure p can be calculated using, for example, the methods described in Warpinski and Teufel. The stress σ _x , which affects the width, can be calculated from:

Where

- координаты и расстояния из фиг. 2, нормированные на полувысоту h/2 трещины. Поскольку σ_х изменяется в направлении у, а также в направлении х, напряжение, усредненное по высоте трещины, можно использовать при вычислении тени напряжения.and where σ _x is the stress in the x direction, p is the internal pressure, and

- coordinates and distances from FIG. 2, normalized to half maximum h / 2 cracks. Since σ _x varies in the y direction, as well as in the x direction, the stress averaged over the height of the crack can be used in calculating the stress shadow.

The analytical equation given above can be used to calculate the average effective stress of a single crack acting on an adjacent parallel crack, and it can be included in the effective closing stress acting on this crack.

Cracks can be oriented in different directions and can intersect with each other in systems of more complex cracks. In FIG. 3.1 shows a system 300 of complex cracks displaying stress shadow effects. The fracture system 300 includes hydraulic fractures 303 extending from the borehole 304 and interacting with other fractures 305 in the fracture system 300.

A more general method can be used to calculate the effective stress acting on any branch of a crack from the rest of the crack system. In an unconventional model of cracks, the mechanical interactions between cracks can be modeled using the two-dimensional method of discontinuous displacements (DLS) (Olson 2004) to calculate induced stresses (see, for example, Fig. 3.1).

Two-dimensional solution of discontinuous displacements in plane deformation (see, for example, Crouch SL and Starfield AM, Boundary element methods in solid mechanics, George Allen and Unwin Ltd, London, Fisher, MK (1983) (hereinafter Crouch and Starfield 1983), complete the content of the source is incorporated into this application by reference) can be used to describe the normal and shear stresses (σ _n and σ _x ) acting on one element of the crack induced by discontinuous revealing and shear displacements (D _n and D _s ) from all elements of the crack. To take into account the three-dimensional effect due to the finite crack height, the Olson 2004 approach can be used to obtain a three-dimensional correction coefficient for the influence coefficients C ^ij in combination with modified elasticity equations from the two-dimensional method of discontinuous displacements:

where A is the matrix of influence coefficients presented in equation (9), N is the total number of elements in the system whose interaction is taken into account, i is the element in question and j = 1, N are other elements in the system whose influence on the voltage of element i is calculated; and where C ^ij are the two-dimensional coefficients of the effect of elasticity during plane deformation. These expressions can be found in Crouch and Starfield 1983.

Elements i and j in FIG. Figure 3.1 schematically shows the variables i and j from equation (8). Gaps D _s and D _n related to element j are also shown in FIG. 3.2. D _n may be the same as the slot width, and shear stress s may be 0, as shown. The discontinuity discontinuity of the element j creates a voltage on the element i, shown as σ _s and σ _n .

The three-dimensional correction factor proposed in Olson 2004 can be represented as follows:

where h is the crack height, d _ij is the distance between elements i and j, α and β are adjustable parameters. Equation (9) shows that a three-dimensional correction factor can lead to a weakening of the interaction between any two elements of the crack with increasing distance.

,

. При подстановке этих двух условии в уравнение (8) можно найти разрывы (D_s) сдвиговых смещений и нормальное напряжение (σ_n), наводимое на каждый элемент трещины.In the unconventional model of cracks, at each time step, additional induced stresses due to stress shadow effects can be calculated. It can be assumed that at any time, the gap width is equal to the normal discontinuity discontinuities (D _n ), and the shear stress on the surface of the crack is zero, i.e.

,

. Substituting these two conditions into equation (8), one can find discontinuity discontinuities (D _s ) and normal stress (σ _n ) induced on each element of the crack.

The influence of stresses induced by the stress shadow on the picture of the development of a system of cracks can be described in two ways. First, during the iteration of pressure and width, the initial local stresses on each element of the crack can be modified by adding the normal stress due to the effect of the stress shadow. This can directly affect the fracture pressure and the width distribution, which can lead to a change in crack growth. Secondly, when the stresses induced by the stress shadow (normal and shear stresses) are turned on, the local stress fields in front of the developing ends can also change, which can cause a deviation of the direction of the local principal stress from the initial direction of the local stress. This variable direction of the local principal stress can lead to the rotation of the crack from the initial plane of development and can also affect the picture of the development of the system of cracks.

Validation of the voltage shadow model

The validation of the unconventional model of cracks for cases of cracks with two wings can be performed using, for example, the methods of Weng 2011 or Kresse 2011. In addition, the validation can be performed using the method of modeling the stress shadow. As suggested, for example, in Itasca Consulting Group Inc., 2002, FLAC3D (Fast Lagrangian Analysis if Continua in 3 Dimensions), Version 2.1, Minneapolis: ICG (2002) (hereinafter “Itasca 2002”), the results of the two-dimensional discontinuous displacement method can be compare with the results of a three-dimensional fast Lagrange analysis of continuous media.

Comparison of the advanced two-dimensional method of discontinuous displacements with three-dimensional fast Lagrange analysis of continuous media

The three-dimensional correction factors proposed in Olson 2004 contain two empirical constants, α and β. The values of α and β can be calibrated by comparing the stresses obtained as a result of numerical solutions (by the improved two-dimensional method of discontinuous displacements) with the stresses from the analytical solution for a plane-deformed crack with infinite length and infinite height. The reliability of the model can be additionally verified by comparing the results for two parallel rectilinear cracks with a finite length and height from a two-dimensional model of discontinuous displacements with full three-dimensional numerical solutions using, for example, three-dimensional fast Lagrange analysis of continuous media.

The validation task is shown in FIG. 4. In FIG. 4 is a schematic diagram 400 for comparing an advanced two-dimensional method of discontinuous displacements with a three-dimensional fast Lagrange analysis of continuous media in the case of two parallel rectilinear cracks. As shown in FIG. 4, two parallel cracks 407.1, 407.2 are exposed to stresses σ _x , σ _y along the x-axis, y coordinates. The cracks have a length of 2L _xf and a _burst pressure p ₁ , r ₂ , respectively. Cracks are at a distance s from each other.

In the three-dimensional fast Lagrange analysis of continuous media, a crack can be modeled as two surfaces in the same place, but with no grid points attached. Constant internal fluid pressure can be applied to the grids as normal stress. In addition, cracks can be exposed to distant stresses, σ _x and σ _y . Two cracks can have the same length and height with a height to half ratio of 0.3.

You can compare stresses along the k axis (y = 0) and the y axis (x = 0). As shown for comparison in FIG. 5.1-5.3, two closely spaced cracks can be simulated (s / h = 0.5). These figures are given to compare the advanced two-dimensional method of discontinuous displacements and three-dimensional fast Lagrange analysis of continuous media: stresses along the x axis (y = 0) and the y axis (x = 0).

These figures include graphs 500.1, 500.2, 550.3, respectively, illustrating σ _y along the y axis, σ _x along the y axis, and σ _y along the x axis, respectively, for extended cracks obtained by the two-dimensional method of discontinuous displacements and three-dimensional fast Lagrange analysis of continuous wednesday In FIG. Figure 5.1 shows graphs of σ _x / p (along the y axis) versus the normalized distance from the crack (along the x axis) obtained using the two-dimensional method of discontinuous displacements (DLS) and three-dimensional fast Lagrange analysis of continuous media (TBALNS). In FIG. Figure 5.2 shows graphs of σ _x / p (along the y axis) versus the normalized distance from the crack (along the x axis) obtained using the two-dimensional method of discontinuous displacements (DLS) and three-dimensional fast Lagrange analysis of continuous media (TBALNS). In FIG. Figure 5.3 shows graphs of σ _y / p (along the y axis) versus the normalized distance from the crack (along the x axis) obtained using the two-dimensional method of discontinuous displacements (DLS) and three-dimensional fast Lagrange analysis of continuous media (TBALNS). The position L _{f of the} end of the crack is shown along the x / h line.

As shown in FIG. 5.1-5.3, the stresses modeled on the basis of the advanced two-dimensional method of discontinuous displacements using the three-dimensional correction factor are very well consistent with the stresses from the results of the full three-dimensional simulation model, which show that the correction coefficient allows to obtain a three-dimensional effect based on the height of the crack in the stress field.

Comparison with CSIRO Model

The validity of an unconventional model of cracks, which includes an advanced two-dimensional method of discontinuous displacements, can be verified by comparing with the full two-dimensional simulation model of discontinuous displacements from CSIRO (Organization of the Commonwealth for Scientific and Industrial Research) (see, for example, Zhang X., Jeffrey RG and Thiercelin M., 2007, "Deflection and propagation of fluid-driven fractures at frictional bedding interfaces: A numerical investigation", Journal of Structural Geology, 29: 396-410 (hereinafter "Zhang 2007"), the full contents of the source are included in this application by reference). This approach can be used, for example, in the limited case of a very large crack height, since the three-dimensional effects of crack height are not taken into account in the two-dimensional method of discontinuous displacements.

A comparison of the influence of two closely developing cracks on other development paths can be used. The development of two hydraulic fractures that occur parallel to each other (development in the direction of the local maximum stress) can be modeled for such configurations as: 1) initiation points on tops of each other and distance from each other under isotropic stress; and 2) anisotropic far field voltages. The crack propagation path and pressure inside each fracture for the input data given in Table 1 can be compared for an unconventional fracture model and CSIRO code.

When two cracks initiate parallel to each other when the initiation points are separated by dx = 0, dy = 33 feet (10.1 m) (the maximum horizontal stress field is oriented in the x direction), they can deviate from each other due to the stress shadow effect.

The development paths in the case of isotropic and anisotropic stress fields are shown in FIG. 6.1 and 6.2. These figures are graphs 600.1 and 600.2, showing the development paths of two initially parallel cracks 609.1 and 609.2 in isotropic and anisotropic stress fields, respectively. Cracks 609.1 and 609.2 are initially parallel near injection points 615.1, 615.2, but diverge as they move away from them. When compared with the isotropic case, it is seen that the curvature of the cracks is less in the case of stress anisotropy. This may be due to competition between the stress shadow effect, which tends to deflect the cracks from each other, and the far field stresses that propel the cracks to develop in the direction of maximum horizontal stress (in the x direction). The influence of stress in the far field becomes dominant as the distance between the cracks increases, and in this case, cracks can tend to develop in parallel in the direction of the maximum horizontal stress.

In FIG. Figures 7.1 and 7.2 are graphs 700.1, 700.2 showing a pair of cracks initiated from two different injection points 711.1, 711.2, respectively. These figures show, for comparison, the initiation of cracks from points spaced dx = dy = 10.1 m for isotropic and anisotropic stress fields, respectively. In these figures, for cracks 709.1 and 709.2, there is a tendency to propagate to each other. Examples of similar behavior were observed in laboratory experiments (see, for example, Zhang 2007).

As shown above, an improved two-dimensional method of discontinuous displacements, implemented in an unconventional model of cracks, can capture three-dimensional effects of a finite height of cracks from the picture of interaction and development of cracks, and at the same time, the method is computationally efficient. One can get a good estimate of the stress field for a system of vertical hydraulic fractures and (picture) the direction of the development of cracks.

Case examples

Case No. 1, parallel fractures in horizontal wells

In FIG. 8 is a graphical representation of 800 parallel transverse cracks 811.1, 811.2, 811.3, developing simultaneously from multiple clusters 815.1, 815.2, 815.3 perforations, respectively, around a horizontal borehole 804. In each of the cracks 811.1, 811.2, 811.3, different speeds q ₁ , q ₂ , q ₃ flows, which are part of the total flow q _t at a pressure p ₀ .

When the reservoir conditions and perforations are the same for all cracks, the cracks can be approximately the same size if the friction pressure loss in the borehole between the perforation clusters is proportionally small. This can be assumed when the cracks are spread out over sufficiently large distances and the effects of the stress shadow are negligible. When the distances between the cracks are in the region of influence of the stress shadow, it can affect not only the crack width, but also another crack dimension. To illustrate this, a simple example of five parallel cracks can be considered.

In this example, the cracks are assumed to have a constant height of 100 feet (30.5 m). The distance between the cracks is 65 feet (19.8 m). Other input parameters are given in table 2.

In this simple case, the usual Perkins-Kern-Nordgren (PCN) model (see, for example, Mack MG and Warpinski NR, "Mechanical of Hydraulic Fracturing", Chapter 6, "Reservoir Stimulation", 3rd Ed., Eds. Economides MJ and Nolte KG, John Willey and Sons (2000)) for numerous cracks can be modified by including the calculation of the stress shadow taken from equation (6). The increase in closure stress can be approximated by averaging the stress calculated over equation (6) over the entire crack. Note that in this simplified Perkins-Kern-Nordgren model it is not possible to simulate the rotation of cracks due to the stress shadow effect. The results from this simple model can be compared with the results from an unconventional model of cracks, which includes pointwise calculation of the stress shadow along all crack paths, as well as crack rotation.

In FIG. Figure 9 shows the results of modeling the length of five cracks calculated on the basis of both models. In FIG. 9 is a graph 900 showing the length (along the y axis) versus time (t) of five parallel cracks during injection. Lines 917.1-917.5 are derived from an unconventional model of cracks. Lines 919.1-919.5 are derived from the simplified Perkins-Kern-Nordgren model.

Crack geometry and width contours from an unconventional crack model for the five cracks of FIG. 9 are shown in FIG. 10. In FIG. 10 is a schematic representation 1000 showing cracks 1021.1-1021.5 near borehole 1004.

Crack 1021.3 is the middle crack of the five cracks, and cracks 1021.1 and 1021.5 are the most extreme cracks. Since cracks 1021.2, 1023.3, and 1021.4 have a smaller width than the width of the extreme cracks, due to the effect of the shadow of stress, they can exert greater resistance to flow, perceive a lower flow velocity and have shorter lengths. Therefore, in the dynamic mode, the stress shadow can affect not only the crack width, but also the crack length.

The influence of the stress shadow on the crack geometry can be influenced by many parameters. To illustrate the effect of some of these parameters, the calculated crack lengths for various crack spacings, pressure drops on perforations, and stress anisotropies are shown in Table 3.

In FIG. 11.1 and 11.2 show the geometry of the cracks obtained by predicting using an unconventional model of cracks for the case of a large drop in pressure on the perforations and the case of a large separation of cracks (for example, about 120 feet (36.6 m)). In FIG. 11.1 and 11.2 are schematic diagrams of 1100.1 and 1100.2, showing five cracks 1123.1-1123.5 near borehole 1104. When the pressure drop across the perforations is large, a large deflecting force can be created, due to which the flow velocity will be unevenly distributed over all clusters of perforations. Consequently, the stress shadow can weaken, and the resulting crack lengths can become approximately equal to those shown in FIG. 11.1. When the crack spacing is large, the effect of the stress shadow can dissipate and the cracks can have approximately the same dimensions shown in FIG. 11.2.

Case No. 2, complex cracks

In the example of FIG. 12 an unconventional model of fractures was used to simulate a 4-stage hydraulic fracturing operation in a horizontal well in a clay formation. See, for example, Cipolla C, Weng X., Mack M., Ganguly U., Kresse O., Gu H., Cohen C. and Wu R., "Integrating microseismic mapping and complex fracture modeling to characterize fracture complexity", Paper SPE 140185, presented at the SPE Hydraulic Fracturing Conference and Exhibition, Woodlands, Texas, USA, January 24-26, 2011 (hereinafter "Cipolla 2011"), the full contents of the source are incorporated into this application by reference. The well can be cased and cemented and each injection stage is carried out through three or four perforation clusters. At each of the four stages, there may be approximately 25,000 barrels (4,000 m ³ ) of liquid and 440,000 pounds (2 · 10 ⁶ kg) of proppant. Comprehensive data can be obtained in the well, including high-quality acoustic logs that provide an estimate of the minimum and maximum horizontal stress. Microseismic mapped data can be obtained at all stages. See, for example, Daniels J., Waters G., LeCalvez J., Lassek J. and Bentley D., "Contacting more of the Barnett shale through an integration of real-time microseismic monitoring, petrophysics and hydraulic fracture design", Paper SPE 110562, presented at the 2007 SPE Annual Technical Conference and Exhibition, Anaheim, California, USA, October 12-14, 2007. This example is shown in FIG. 12. In FIG. 12 is a graph showing microseismic mapping of microseismic events 1223 near borehole 1204 at various stages.

The stress anisotropy from the high-quality acoustic logging diagram is manifested as a higher stress anisotropy in the lower section of the well compared to the wellhead. Advanced 3D Interpretation

Seismic data shows that the prevailing direction of natural fractures in the lower section is oriented from the north-east to the south-west, and at the mouth it changes and is oriented from the north-west to the south-east. See, for example, Rich J.P. and Ammerraan M., "Unconventional geophysics for unconventional plays", Paper SPE 131779, presented at the Unconventional Gas Conference, Pittsburg, Pennsylvania, USA, February 23-25, 2010, the entire contents of the source are incorporated by reference.

The simulation results can be based on an unconventional model of cracks without a complete calculation of the stress shadow (see, for example, Cipolla 2011), including without shear and shear stresses of cracks (see, for example, Weng 2011). As suggested in this application, the model can be updated using the full voltage model. In FIG. 13.1-13.4 shows a plan view of a simulated fracture system 1306 near a borehole 1304 for all four stages, respectively, and corresponding microseismic measurements 1323.1-1323.4 are shown for comparison.

From the simulation results in FIG. 13.1-13.4 it can be seen that in stages 1 and 2 closely spaced cracks do not diverge significantly. This may be due to high stress anisotropy in the lower section of the borehole. In steps 3 and 4, in which the stress anisotropy is less, a larger crack difference can be seen resulting from the stress shadow effect.

Case No. 3, a multi-stage example

Case No. 3 is an example showing how the stress shadow from the preceding stages can affect the pattern of the development of a hydraulic fracture system in the next stages of formation stimulation, leading to a change in the overall picture of the formed hydraulic fracture system in the case of a four-stage stimulation.

This case includes four stages of a hydraulic fracturing operation. The well is cased and cemented. At stages 1 and 2, they pump through three perforated clusters, and at stages 3 and 4, they are pumped through four perforated clusters. The structure of the rock is isotropic. The input parameters are listed in table 4 below. Top views of the complete hydraulic fracture system with and without the stress shadow from the previous steps are shown in FIG. 13.1-13.4.

In FIG. 14.1-14-4 are schematic diagrams of 1400.1-14 00.4 showing a fracture system 1429 at various stages during a fracturing operation. In FIG. 14.1 shows a system of 1429 discrete fractures (SDT) before stimulation. In FIG. 14.2 shows a simulated system of 1429 discrete fractures after the first stage of stimulation. Due to the first stage of stimulation, the discrete fracture system 1429 has developed fractures 1431 hydraulic fracturing (TGR), continuing from it. In FIG. Figure 14.3 shows a system of discrete fractures with simulated hydraulic fractures 1431.1-1431.4, which developed during the corresponding four stages, but without taking into account the influence of the previous stages. In FIG. 14.4 shows a system of discrete cracks with the image of hydraulic fractures 1431.1, 1431.2′-1431.4 ′ that developed during four stages, but without taking into account the influence of stress shadows and hydraulic fractures from the previous stages on the cracks.

When the steps are performed separately, then, as shown in FIG. 14.3, they can not be imagined relative to each other. When the stress shadow and hydraulic fractures from the previous steps are taken into account, as in FIG. 14.4, the picture of development is subject to change. Hydraulic fracture cracks 1431.1 formed in the first stage are the same in both cases shown in FIG. 14.3 and 14.4. The first stage can influence the development pattern at the second stage 1431.2 through the stress shadow, as well as through the new discrete crack system (including through the hydraulic fracture 1431.1 from stage 1), which leads to a change in the hydraulic fracture development patterns 1431.2 ′ . Hydraulic fracture crack 14 31.1 ′ may begin to repeat the hydraulic fracture 1431.1 formed in step 1 when it is taken into account. In the third step, 1431.3 can repeat the hydraulic fracture formed during the second step 1432.2, 1431.2 ′ of the formation impact, and there can be no development over a very large distance due to the effect of the stress shadow from the second step, as shown by 1431.3 in comparison with 1431.3 ′. For the fourth stage (1431.4), there may be a tendency to rotate compared to the third stage, when possible, but there may be a repeat of the hydraulic fracture 1431.3 ′ from the previous stages when the collision occurs, and this is indicated by the hydraulic fracture 1431.4 ′ in FIG. 14.4.

A method for calculating the stress shadow in a system of complex hydraulic fractures is proposed. The method may include an improved two-dimensional or three-dimensional method of discontinuous displacements with correction for the influence of the final height of the cracks. The method can be used to approximate the interaction between different branches of cracks in a system of complex cracks for the fundamental solution of the three-dimensional problem of cracks. This calculation of the stress shadow can be included in an unconventional model of cracks, a complex model of a crack system. The results for simple cases of two cracks show that, depending on the initial relative positions, the cracks can be attracted or repelled from each other, and the results are quite comparable with the results from an independent two-dimensional model of non-planar hydraulic fractures.

Simulations of multiple parallel cracks from a horizontal crack can be used to validate the properties of the two most extreme cracks, which can be more defining, while internal cracks are shorter in length and width due to the stress shadow effect. In addition, these properties may depend on other parameters, such as the pressure drop across the perforations and the distance between the cracks. When the distance between the cracks is greater than the height of the cracks, the effect of the stress shadow can weaken and there may be slight differences between the many cracks. When the pressure drop across the perforations is large, a significant deviation from the uniform flow distribution over the perforation clusters can be created and the size of the cracks can become approximately equal regardless of the effect of the stress shadow.

If the layers have a small stress anisotropy when creating complex cracks, the interaction of the cracks can lead to a strong divergence of the cracks when they tend to push off from each other. On the other hand, with large stress anisotropy, there may be limited crack divergence, when stress anisotropy weakens the phenomenon of crack rotation due to the stress shadow, and the crack can be forced to propagate in the direction of maximum stress. Regardless of the degree of crack divergence, stress shadowing can affect the crack width, which can affect the distribution of injection rates across multiple perforation clusters, the total area occupied by the crack system, and proppant placement.

In FIG. 15 is a flowchart of a method 1500 for performing hydraulic fracturing operations at a well location, such as the well location 100 of FIG. 1.1. The location of the well is in an underground formation having a borehole passing through it and a system of fractures. The crack system has natural cracks shown in FIG. 1.1 and 1.2. The method (1500) may include performing (1580) the operation of stimulating the well by exciting the location of the well by pumping fluid together with proppant into the fracture system to form a hydraulic fracture system. In some cases, the stimulation can be performed at the location of the well or by modeling.

The method includes obtaining (1582) data on the location of the well and a mechanical model of the geological environment for the subterranean formation. Data on the location of the well may include any data on the location of the well that may be useful in modeling, such as parameters of natural fractures, images of a fracture system, etc. Natural fracture parameters may include, for example, orientation, density distribution, and mechanical properties (e.g., friction coefficients, connectivity, resistance to crack propagation, etc. The parameters of fractures can be obtained from direct observations of downhole log images, evaluation of three-dimensional seismic surveys, an algorithm for tracking the movement of ants, estimating the anisotropy of sound waves, the curvature of the geological layer, microseismic events or images, etc. Examples of methods for obtaining crack parameters, see PCT / US 2012/48871 and US 2008/0183451, the full contents of which are incorporated herein by reference.

Images can be obtained, for example, by observing well logs, estimating fracture sizes based on well measurements, microseismic imaging and / or the like. Crack sizes can be estimated by analyzing seismic measurements, using an algorithm for tracking the movement of ants, and evaluating acoustic measurements, geological measurements and / or similar. In addition, other data on the location of the well can be obtained from various sources, such as measurements at the location of the well, historical data, assumptions, etc. Such data may include, for example, completion data, geological structure, petrophysical, geomechanical, logging and other types of data. A mechanical model of the geological environment can be obtained using conventional methods.

Method (1500) also includes the formation (1584) of a fracture growth pattern of hydraulic fracture over time, for example, during a well stimulation operation. In FIG. 16.1-16.4 shows an example of the formation (1584) of a pattern of growth of hydraulic fractures. As shown in FIG. 16.1, in the initial state, natural fracture system 1606.1 1623 is located in the subterranean formation 1602 with a borehole 1604 therein. When the proppant is injected into the subterranean formation 1602 from the borehole 1604, proppant pressure creates hydraulic fractures 1691 around the borehole 1604. Hydraulic fractures 1691 propagate into the underground formation along L ₁ and L ₂ (FIG. 16.2) and, as shown in FIG. 16.2-16 - 3, with the course they meet with other cracks in the system of 1606.1 cracks. Contact points with other cracks are intersections 1625.

Formation (158 4) may include the propagation (158 6) of hydraulic fractures from the borehole and into the fracture system of the subterranean formation to form a hydraulic fracture system including the natural fractures and hydraulic fractures shown in FIG. 16.2. The pattern of crack growth is based on the parameters of natural cracks and the minimum stress and maximum stress acting on the subterranean formation. The formation may also include determining (1588) the parameters of hydraulic fractures (e.g., pressure p, width w, flow rate q, etc.), determining (1590) the transfer parameters for the proppant passing through the hydraulic fracturing system, and determination (1592) of the sizes (e.g., height) of hydraulic fractures based on, for example, certain parameters of hydraulic fractures, certain transfer parameters, and a mechanical model of the geological environment. The parameters of hydraulic fractures can be determined after propagation. In addition, determination (1592) can be performed based on proppant transfer parameters, well location parameters, and other data elements.

Education (1584) may include modeling rock properties based on a mechanical model of the geological environment described, for example, in Koutsabeloulis and Zhang, "3D reservoir geomechanics modeling in oil / gas field production", SPE Paper 126095, 2009 SPE Saudi Arabia Section Technical Symposium and Exhibition held in Al Khobar, Saudi Arabia, May 9-11, 2009. In addition, the formation may include modeling of a hydraulic fracturing operation using well location data, fracture parameters, and / or images as input to software for a model such as unconventional Split cracks to obtain successive images of induced hydraulic fractures in the fracture system.

In addition, method (1500) may include performing (1594) shading stresses relative to hydraulic fractures to determine the mutual influence of hydraulic fractures (or effects on other cracks) and repeating (1598) formation (1584) based on stress shading and / or a certain mutual influence of hydraulic fractures. Repetition can be performed to take into account the mutual influence of cracks, which can affect the growth of cracks. The implementation of stress shadowing may include, for example, performing a two-dimensional or three-dimensional method of discontinuous displacements for each of the hydraulic fractures and updating the pattern of crack growth over time. The pattern of crack growth can propagate perpendicular to the local main stress direction in accordance with the voltage shadowing. The pattern of crack growth may include the effects of natural cracks and hydraulic fractures on the crack system (see FIG. 16.3).

Voltage shading can be performed for multiple boreholes at the location of the wells. Voltage shading from different boreholes can be combined to determine the interaction of cracks for each of the boreholes. The formation can be repeated for each of the voltage shades carried out for one or more of the numerous boreholes. In addition, the formation can be repeated to obscure the stress carried out when performing simulation taking into account numerous boreholes. In addition, multiple simulations can be performed on the same borehole with various data combinations and compared if desired. Historical and other data can also be entered into the education phase in order to receive multiple sources of information for consideration in the final results.

Furthermore, the method includes determining (1596) the nature of the intersection of hydraulic fractures and an encounter if the hydraulic fracture meets another crack, and repeating (1598) the formation (1598) based on the intersection if the hydraulic fracture meets the crack (see, for example, Fig. 16.3). The nature of the intersection can be determined using, for example, the methods from PCT / US 2012/059774, the entire contents of which are incorporated into this application by reference.

Determining the nature of the intersection may include performing voltage shading. Depending on the well conditions, the pattern of crack growth may or may not change when a hydraulic fracture meets a crack. When the hydraulic fracture pressure is greater than the stress acting on the encountered crack, the pattern of crack growth can propagate along the encountered crack. The pattern of crack growth can propagate along the crack encountered until the end of the natural crack is reached. The direction of the pattern of crack growth can change at the end of a natural crack, and, as shown in FIG. 16.4, the pattern of crack growth will continue in the direction perpendicular to the minimum stress at the end of the natural crack. As shown in FIG. 16.4, the hydraulic fracture propagates along a new trajectory 1627 in accordance with local stresses σ ₁ and σ ₂ .

Optionally, method (1500) may include verifying (1599) the validity of the crack growth pattern. Validation can be performed by comparing the resulting growth pattern with other data, such as microseismic images shown, for example, in FIG. 7.1 and 7.2.

The method can be performed in any order and, if necessary, repeat. For example, the steps of formation (1584) - (1599) can be repeated over time, for example, in accordance with the iteration, when the system of cracks changes. Education (1584) can be performed to update the iterated modeling performed during education to take into account the interactions and effects of multiple cracks when a system of cracks is modeled over time.

Although the present disclosure has been described with reference to examples of embodiments and implementations, the present disclosure is not limited to such examples of embodiments and / or implementations. More specifically, in systems and methods of the present disclosure, various modifications, changes and / or improvements are allowed without departing from the essence or scope of the present disclosure. In accordance with this scope of the present disclosure, all such modifications, changes, and improvements are certainly covered.

It should be noted that in the development of any such relevant implementation option or multiple implementations, specific decisions must be made to achieve the specific intentions of the developer, such as coordination with the limitations associated with the system and related to business activities that vary from one implementation to another. In addition, it should be understood that such developments can be complex and time-consuming, but nevertheless should be commonplace for those skilled in the art who benefit from this disclosure. In addition to this, the embodiments used disclosed in this application may also include some components other than those listed.

In the description, each numerical value should be read once as modified by the term “about” (unless it is already definitely modified in this way) and then read again as unmodified, unless otherwise indicated. In addition, it should be understood that in the description for any range, given or indicated as used, suitable or similar, it is assumed that any or every value in the range, including the start point and end point, is considered to be precisely defined. For example, “a range of 1 to 10” should be read as showing each and every possible number throughout the continuum between about 1 and about 10. Thus, even if specific data points in a range or data points outside a range are explicitly identified or assigned to several specific points, it should be assumed and understood that any and all data points in the range are considered to be precisely defined and that there is information about the entire range and all points in the range.

The provisions set forth in this application merely provide information relevant to the present disclosure, and may not represent the prior art, but may characterize some embodiments illustrating the invention. All sources cited in this application are fully incorporated into this application by reference.

Although only a few examples of embodiments have been described in detail above, those skilled in the art will readily understand that numerous modifications are possible in the examples of embodiments without substantially deviating from the system and method for performing well stimulation work. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. In the claims, the phrases “agent plus function” are intended to encompass the structures described in this application at the time the function is described, and not only structural equivalents, but also equivalent structures. Thus, although the nail and screw cannot be structural equivalents because the cylindrical surface in the nail is used to fasten the wooden parts together, while the screw uses a screw surface, in the situation of fastening the wooden parts, the nail and screw can be equivalent structures. The applicant’s clear purpose is to not refer to Section 35 of the US Code, §112, paragraph 6, for any limitations of any of the claims except those that specifically use the words “means for” together with the corresponding function.

Claims (17)

1. The method of performing the hydraulic fracturing operation at the location of the well, the location of the well is in an underground formation having a borehole and a fracture system, the fracture system contains natural fractures, the location of the well is excited by pumping the injected fluid together with proppant into the fracture system, this method comprises the steps in which:
receive data on the location of the well containing the parameters of natural fractures, and get a mechanical model of the geological environment for the underground reservoir;
form a picture of the growth of hydraulic fractures for a system of cracks over time, while the formation contains:
the propagation of hydraulic fractures from the borehole and into the fracture system of the subterranean formation to form a hydraulic fracture system containing natural and hydraulic fractures;
determination of parameters of hydraulic fractures after propagation;
determination of transfer parameters for proppant passing through a system of hydraulic fractures; and
determination of the size of hydraulic fractures based on certain parameters of hydraulic fractures, certain transfer parameters and a mechanical model of the geological environment; and
carry out voltage shading relative to hydraulic fractures in order to determine the mutual influence of stresses between hydraulic fractures; and
repeat the formation on the basis of a certain mutual influence of stresses. 2. The method according to claim 1, additionally containing, if hydraulic fractures meet another crack, determining the nature of the intersection with the other crack encountered, and in which the repetition comprises the repetition of formation based on a certain mutual influence of stresses and the nature of the intersection. 3. The method according to claim 2, in which the growth pattern of hydraulic fractures does not change under the influence of the nature of the intersection. 4. The method according to claim 2, in which the pattern of crack growth changes under the influence of the nature of the intersection. 5. The method according to claim 2, in which the hydraulic fracture pressure of the hydraulic fracture system is greater than the stress acting on the encountered crack, and in which the pattern of crack growth propagates along the encountered crack. 6. The method according to claim 1, in which the pattern of crack growth continues to propagate along the encountered crack until it reaches the end of the natural crack. 7. The method according to claim 1, in which the crack growth pattern changes direction at the end of a natural crack, while the crack growth pattern continues in a direction perpendicular to the minimum stress at the end of the natural crack. 8. The method according to claim 1, in which the pattern of crack growth propagates perpendicular to the local main stress in accordance with the shadowing voltage. 9. The method according to claim 1, wherein the voltage shadowing comprises performing displacement fracture for each of the hydraulic fractures. 10. The method according to claim 1, wherein the voltage shading comprises performing voltage shading around multiple boreholes from the location of the wells and repeating the formation using voltage shading performed relative to the numerous boreholes. 11. The method according to claim 1, in which the voltage shading comprises the implementation of voltage shading at numerous stages of excitation in the borehole. 12. The method according to claim 1, additionally containing verification of the authenticity of the pattern of growth of cracks. 13. The method of claim 12, wherein the validation comprises comparing the crack growth pattern with at least one simulation from simulations of the crack system. 14. The method according to claim 1, wherein the propagation comprises the propagation of hydraulic fractures along the entire pattern of growth of hydraulic fractures based on the parameters of natural fractures and the minimum stress and maximum stress acting on the subterranean formation. 15. The method according to claim 1, in which the determination of the size of the cracks contains one of the evaluation of seismic measurements, an algorithm for tracking the movement of ants, acoustic measurements, geological measurements and combinations thereof. 16. The method according to claim 1, in which the data on the location of the well contain at least one of geological, petrophysical, geomechanical data, data logging measurements, completion, historical data and combinations thereof. 17. The method according to claim 1, in which the parameters of natural fractures are formed in accordance with one of the observation of downhole logging images, estimating the size of the cracks based on downhole measurements, obtaining microseismic images and combinations thereof.

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